A two-dimensional numerical investigation of the oscillatory flow behaviour in rectangular fire compartments with a single horizontal ceiling vent

This paper presents a comparison of fire field model predictions with experiment for the case of a fire within a compartment which is vented (buoyancydriven) to the outside by a single horizontal ceiling vent. Unlike previous work, the mathematical model does not employ a mixing ratio to represent vent temperatures but allows the model to predict vent temperatures a priori. The experiment suggests that the flow through the vent produces oscillatory behaviour in vent temperatures with puffs of smoke emerging from the fire compartment. This type of flow is also predicted by the fire field model. While the numerical predictions are in good qualitative agreement with observations, they overpredict the amplitudes of the temperature oscillations within the vent and also the compartment temperatures. The discrepancies are thought to be due to three-dimensional effects not accounted for in this model as well as using standard ‘practices’ normally used by the community with regards to discretization and turbulence models. Furthermore, it is important to note that the use of the k–ε turbulence model in a transient mode, as is used here, may have a significant effect on the results. The numerical results also suggest that a linear relationship exists between the frequency of vent temperature oscillation (n) and the heat release rate (Q0) of the type n∝Q0.290, similar to that observed for compartments with two horizontal vents. This relationship is predicted to occur only for heat release rates below a critical value. Furthermore, the vent discharge coefficient is found to vary in an oscillatory fashion with a mean value of 0.58. Below the critical heat release rate the mean discharge coefficient is found to be insensitive to fire size.

Buoyancy driven flow and its stability in a horizontal rectangular channel with an arbitrary oriented transversal magnetic field

An MHD flow is considered which is relevant to horizontal Bridgman technique for crystal growth from a melt. In the unidirectional parallel flow approximation an analytical solution is found accounting for the finite rectangular cross section of the channel in the case of a vertical magnetic field. Numerical pseudo-spectral solutions are used in the cases of arbitrary magnetic field and gravity vector orientations. The vertical magnetic field (parallel to the gravity) is found to be he most effective to damp the flow, however, complicated flow profiles with "overvelocities" in the comers are typical in the case of a finite cross-section channel. The temperature distribution is shown to be dependent on the flow profile. The linear stability of the flow is investigated by use of the Chebyshev pseudospectral method. For the case of an infinite width channel the transversal rolls instability is investigated, and for the finite cross-section channel the longitudinal rolls instability is considered. The critical Gr number values are computed in the dependence of the Ha number and the wave number or the aspect ratio in the case of finite section.

Narrating the archive and archiving narrative: the electronic book and the logic of the index

The creation of my hypermedia work Index of Love, which narrates a love story as an archive of moments, images and objects recollected, also articulated for me the potential of the book as electronic text. The book has always existed as both narrative and archive. Tables of contents and indexes allow the book to function simultaneously as linear narrative and non-linear, searchable database. The book therefore has more in common with the so-called 'new media' of the 21st century than it does with the dominant 20th century media of film, video and audiotape, whose logic and mode of distribution are resolutely linear. My thesis is that the non-linear logic of new media brings to the fore an aspect of the book - the index - whose potential for the production of narrative is only just beginning to be explored. When a reader/user accesses an electronic work, such as a website, via its menu, they simultaneously experience it as narrative and archive. The narrative journey taken is created through the menu choices made. Within the electronic book, therefore, the index (or menu) has the potential to function as more than just an analytical or navigational tool. It has the potential to become a creative, structuring device. This opens up new possibilities for the book, particularly as, in its paper based form, the book indexes factual work, but not fiction. In the electronic book, however, the index offers as rich a potential for fictional narratives as it does for factual volumes. [ABSTRACT FROM AUTHOR]